The present invention relates generally to a type of gas turbine engine known as an aircraft bypass turbofan engine, and more particularly to an engine subassembly which provides ground deceleration (such as thrust reversing) for the aircraft.
A gas turbine engine includes a core engine having a high pressure compressor to compress the air flow entering the core engine, a combustor in which a mixture of fuel and the compressed air is burned to generate a propulsive gas flow, and a high pressure turbine which is rotated by the propulsive gas flow and which is connected by a larger diameter shaft to drive the high pressure compressor. A typical aircraft bypass turbofan engine adds a low pressure turbine (located aft of the high pressure turbine) which is connected by a smaller diameter coaxial shaft to drive a front fan (located forward of the high pressure compressor) which is surrounded by a fan nacelle and which may also drive a low pressure compressor (located between the front fan and the high pressure compressor). The low pressure compressor sometimes is called a booster compressor or simply a booster. A flow splitter, located between the fan and the first (usually the low pressure) compressor, separates the air which exits the fan-into a core engine airflow and a surrounding bypass airflow. The bypass airflow from the fan exits the fan nozzle (also called the fan bypass nozzle or the fan exhaust nozzle) to provide most of the engine thrust (in the case of a high bypass engine) for the aircraft. Some of the engine thrust comes from the core engine airflow after it flows through the low and high pressure compressors to the combustor and is expanded through the high and low pressure turbines and accelerated out of the core nozzle (also called the core exhaust nozzle). A core nacelle surrounds the low and high pressure compressors and turbines and the intervening combustor.
Aircraft bypass turbofan engines typically employ thrust reversers for ground deceleration. The term "deceleration" means a negative acceleration such as, but not limited to, slowing down a forward-moving aircraft on the runway or backing an aircraft away from the airport departure gate. Prior art thrust reversers are located in the fan bypass duct (the area radially between the fan and core nacelles and longitudinally between the flow splitter and the fan nozzle). Known designs include cascade and door type thrust reversers. Both designs employ relatively heavy blocker doors with robust actuation systems to block the flow of bypass air from exiting the fan nozzle. A heavy engine is not an efficient engine. What is needed is a lighter turbofan engine subassembly to provide ground deceleration during aircraft landings and to back the aircraft away from the airport departure gate.